Why Do We need A Sewer System

Each time we flush the toilet or wash so that down the sink’s drain,we create sewage (also known in polite society as wastewater).

One question that many people might ask is, “Why not simply dump this waste-water onto the ground outside the house, or into a nearby stream?” There are three main things about wastewater that make it so that you don’t want to release into the environment

Septic Tank

In rural areas where houses are spaced so far apart that a sewer system would be too expensive to install, people install their own, private sewage treatment plants. These are called septic tanks. A septic tank is a key component of the septic system or sewer system.

In North America approximately 25% of the population relies on septic tanks; this can include suburbs and small towns as well as rural areas

Construction Details

Septic Tank Collection System

Tank is designed to prevent directs currents between the tank inlet and outlet. T-pipes or baffles at inlet & outlet with submerged ends to stop currents and retaining the scum. Manhole covers are provided in top slab to permit inspection & maintenance. Top of tank is covered with RCC slab. Sometimes stairs steps are also provided. Provide vent pipe to escape foul gases. Side sump-well with portable pump. Two Compartment Septic Tank.

Design Considerations

CAPACITY OF SEPTIC TANK:-capable of storing sewage flow during detention period &extra volume of sludge for .5 to 3 yrs.

INLET AND OUTLET TEES

DETENTION PERIOD:- 12 to 36 hrs (adopted 24hrs)

LENGTH TO WIDTH RATIO:- Length is 2 to3 times of width.

Working

Sewage enter through the Inlet.

There are three layers

1. Anything that floats rises to the top and forms a layer known as the scum layer.

2. Anything heavier than water sinks to form the sludge layer.

3.In the middle is a fairly clear water layer. This body of water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilizers, but it is largely free of solids.

Potential Problems

Chemicals (pesticides, herbicides)and inorganic materials(paints or solvents)damage the working of a septic tank.

Roots from trees may clog and rupture them.

Excessive water entering the system will overload it and cause it to fail.

Septic tanks by themselves are ineffective at removing nitrogen compounds that can potentially cause algal blooms in receiving waters

All toilet paper are not suitable to dispose in septic tank(some toilet paper was specifically marked as suitable for use in septic systems and some was not).

Environmental Issues

Organic materials +Nutrients = CH4 + CO2 +NH3 +Biomass

Sulfates, under the anaerobic conditions of septic tanks, are reduced to hydrogen sulfide (H2S), a pungent and toxic gas. Nitrates and organic nitrogen compounds are reduced to ammonia. Because of the anaerobic conditions, fermentation processes take place, which ultimately generate carbon dioxide and methane. Methane, a potent greenhouse gas. Waste water also contain phosphate and phosphate can be the limiting nutrient for plant growth in many ecosystems.